A jailed activist in Bahrain on trial for allegedly spreading “false news” is being investigated over a letter published in his name by a French newspaper, authorities said Thursday, the second such probe into his writings in recent months. Nabeel Rajab’s incarceration comes amid an intense crackdown on dissent by the Sunni rulers of Bahrain, a predominantly Shiite island off Saudi Arabia plagued by unrest since its 2011 Arab Spring protests.

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At issue is a letter that appeared Tuesday in Le Monde in Rajab’s name. In it, Rajab asks France and Germany to “be ready to face the monarchies of the Arabian-Persian Gulf” as they “claim to be allies in the battle against extremism while fueling the crisis.” “I am writing from a prison in Bahrain where I expect to be tried for criticizing the bombing of Yemen by Saudi Arabia and for revealing the torture committed in the prisons of my country. For that I risk 15 years in prison,” the letter reads. “My trial is not exceptional, it is ordinary. Thousands of Bahrainis are in prison for expressing criticism and protesting against the government.”

Early Thursday, Bahrain’s Interior Ministry announced an investigation into Rajab over the letter, which it said contained “false rumors and tendentious news that represented an abuse of the Kingdom of Bahrain” and other Gulf countries. The ministry also said Rajab denied writing to the newspaper, an assertion challenged by rights groups supporting the activist. “Nabeel Rajab’s recent letters remind us of Martin Luther King Jr.’s ‘Letter from a Birmingham Jail’,” said Husain Abdulla, executive director of Americans for Democracy & Human Rights in Bahrain, referring the U.S. civil rights icon’s message on nonviolent protest. “Like King, Nabeel is a true champion of human rights.”

Rajab’s lawyer and Bahrain’s government did not immediately respond to requests for comment. Bahrain previously has said “no individual in Bahrain will, or can be, prosecuted for his or her political views due to the freedom of expression protections explicitly stated in the constitution.” But activists say Rajab already faces another charge over a letter published in The New York Times in September. A secular politician also briefly faced charges for speaking to The Associated Press in November during a visit by Britain’s Prince Charles and wife Camilla .

Bahrain, home to the U.S. Navy’s 5th Fleet and an under-construction British naval base, saw protests Wednesday after police clashed with residents of a besieged town that is home to Shiite cleric Isa Qassim, who was stripped of his citizenship in June.